The present invention relates to a wiper bracket for fastening a wiper motor and a wiper bearing for a windshield wiper to the body of a motor vehicle.
Motor vehicle wiper systems are secured to the body of a motor vehicle with a wiper bracket, or so-called elbow plate. The elbow plate has a wiper drive with a wiper motor, whose motor shaft, via connecting rods, drives cranks that are solidly connected to a drive shaft for each window wiper. The drive shaft is supported in a wiper bearing, whose bearing housing is secured to the elbow plate. The wiper bracket is secured directly to a vehicle body via the wiper bearings or via fastening eyelets that are formed onto the wiper bearing, the wiper bracket, and/or a motor bracket.
From German Utility Model DE-U 74 34 119, a wiper bracket is known that is made from a square pipe or tube to which a plate acting as a motor bracket is welded. Such wiper brackets, often also called tubular elbow plates or tubular frame systems, are distinguished by lightweight construction with great stability. For cost reasons, a straight tube is desired, because it requires no preliminary bending operation. The straight version of the tube has high rigidity in the axial direction, which does have a favorable effect in normal wiper system operation, but in the event of a blockage or when there is snow on the window has disadvantages, because the other components of the wiper system, such as the wiper bearings or wiper levers, are heavily loaded, because the tube has such low elasticity. These other components must therefore be reinforced. The attendant higher costs cancel out the cost advantage of the straight tube or make it even more expensive then the alternative.
A wi is also known from European Patent disclosure EP B1 0 409 944, in which tubular elements connect a motor bracket to the wiper bearings via positive-engagement connections. Noise-damping, frequency-filtering or noise absorbing adapters are inserted into the essentially straight tubular elements in order to damp noises that are transmitted from the wiper motor via the wiper bracket to the wiper bearings and then to the vehicle body. A variant shows that the tubular wiper bracket is perforated in one region and filled with a noise-absorbing material, which may be foam. In all these provisions, care must be taken not to reduce the stability of the bracket frame excessively.
A method for reshaping tubes into workpieces is also known from the journal xe2x80x9cWerkstatt und Betriebxe2x80x9d Shop and Factory, Carl Hanser Verlag, Munich, 1995, pages 812-815, and the of print from the journal xe2x80x9cMetallumformtechnikxe2x80x9d Metal Reshaping Technology, Claus Dannert Verlag, 1994, entitled xe2x80x9cPrxc3xa4zisions-Werkstxc3xccke in Leichtbauweise, hergestellt durch Innenhochdruck-Umformenxe2x80x9d Lightweight precision workpieces, made by internal-high-pressure reshaping. This method, which is used above all for the automotive industry, employs high pressures. The tubular piece to be reshaped is placed in a split molding tool, into which the desired workpiece shape is machined. The molding tool, which is mounted in a press, is closed by a press slide that operates vertically. The ends of the tubular piece are closed by closing tools, through which a pressure medium is delivered that presses the walls of the tube against the internal tool shape. An axial pressure is exerted on the tube by horizontally acting slides, and this axial pressure is superimposed on the internal pressure. Thus the material that is required for the reshaping is taken not only from the wall thickness of the tubular piece but is also made available by the shortening of the tube. The closing tools are axially fed during the reshaping. Employing such a method for producing a tubular wiper bracket with different cross-sectional shapes is also the subject of an earlier patent application.
According to the invention, the wiper bracket has a longitudinally elastically resilient region between the motor receptacle and the wiper bearing; this region is expediently formed in that the hollow profile in this region has alternating portions with a smaller and a larger diameter. If the flexural strength of the wiper bracket is reduced by this provision, then this can be compensated for according to a feature of the invention in that the mean diameter in the elastically resilient region is increased compared with the diameter in the adjacent regions. The mean diameter is defined as the arithmetic mean between the larger and the smaller diameters. It is essential that the resistance moment, which is decisive for the flexural strength, be increased by an increased outer contour, but without increasing the wall thickness that is definitive for the axial elasticity. The same is true for tubular profiles with a nonround cross section as well.
Because the rigidity in the axial direction is reduced, the peak load in the wiper arm and wiper bearing in the event of blockage or snow on the window is reduced. This applies above all in the region of the parking position and the reversal point of the wiper arm, or the extended and covering position between the crank of the wiper motor and a connecting rod. Since the components subjected to less stress can be smaller in size, there are savings in terms of cost and weight.
Disadvantages that might possibly arise from reduced flexural strength of the axially elastically resilient region can also be overcome by providing that this region is disposed in a portion of the hollow profile that is subjected to only little bending stress. Such regions are formed by straight portions of the hollow profile, which extend essentially parallel to a connecting rod and thus above all absorb tensile and compressive forces.
As a rule, elastically resilient regions will be provided on both sides of the wiper motor. Often, however, it will suffice to dispose an axially elastic region on only the passenger side of the wiper motor. As a result, the wiping quality on the driver""s side is not impaired by the axial elasticity, and nevertheless the components are largely protected against an overload.
The different diameters can expediently be achieved by means of a pressing operation or an internal-high-pressure reshaping process. By pressing, in general only indentations can be made, by which the mean diameter in this region is reversed, but by the internal-high-pressure reshaping process, the diameter of the high-profile can be widened, so that the hollow profile of the wiper bracket can be widened in the region of the alternating diameters and thus gains a higher resistance moment and at the same time a greater axial elasticity.